Rotary kilns are kilns for continuous processes in process engineering and used, for example, as clinker kilns in cement manufacturing plants. The rotary drum of such a kiln is slightly inclined in the longitudinal direction such that the revolution of the kiln cylinder causes an axial transport of the material in the interior of the kiln, namely from the inlet side to the outlet side. Rotary kilns used in the cement industry typically have lengths of 75 to 80 m, but occasionally also reach lengths up to 150 m, and diameters up to 6.5 m. The rotary drum of the rotary kiln features bearing rings that are spaced apart from one another in the axial direction and connected to the rotary drum by means of fastening systems that allow thermal expansions of the rotary drum during the operation of the kiln. The bearing rings are supported on rollers that respectively are supported rotatably about an axis extending in the axial direction of the rotary drum axis. Each bearing ring is usually assigned to two rollers that are arranged at a distance from one another and the rotational axes of which extend parallel to one another. The supporting height and the lateral position can be adjusted by adjusting the distance between two of the rollers that respectively support one bearing ring, wherein it is attempted to adjust the supporting height and the lateral position on all bearing rings in such a way that the rotary drum axis, i.e. the connection between the centres of the circular areas defined by all bearing rings, extends straight over the enbearing ring length of the rotary kiln.
Straightness deviations of the rotary kiln axis that may be caused, for example, by installation tolerances, wear of bearing rings, rollers and roller bearings during the operation of the kiln exert a dynamic bending stress on the rotary drum shell and therefore lead to the risk of cracking and increased abrasion.
Deviations of the parallelism of the rotational axes of the rollers with the rotary kiln axis lead to a significant increase in the friction between the bearing ring and the rollers on the one hand and to an uneven contact between the bearing ring and the rollers on the other hand. Both increase the abrasion and shorten the service life, i.e. the time, over which the rotary kiln can operate without interruption until the next maintenance procedure needs to be carried out.
The service life of a rotary kiln is also decisively influenced by deformations of the rotary drum shell. Such deformations may be created, in particular, due to high temperatures and have no relation whatsoever to the above-described straightness deviations of the rotary drum axis, but rather concern, in particular, local deviations from the straightness of the shell or the shell generatrix and the circularity of the shell cross section. The deformations of the rotary drum shell have negative effects on the refractory lining in the interior of the rotary drum.